The frequency range of a signal calculated from black hole perturbation theory is bounded from above by the innermost stable circular orbit. This corresponds, by virtue of equation (), to an orbital velocity of . In practice there is also a lower bound. Since zero frequency would correspond to an infinite orbital radius we have to introduce a cutoff. In the present data files . Figure shows the allowed frequency range as a function of the total mass .
Since in equation () diverges at calculating at the upper limit is numerically difficult. However this is not a problem in the time domain, since the system spends very little time near . An value of inaccurate by several percent will typically not change the signal by even one wave cycle.